Testing in Java: Best Practices, Tools, and Tips for Developers

Software development is a demanding process that presents engineers with a wide range of challenges, including ensuring that the systems they are building not only work properly but also comply with legal requirements and industry-specific standards while remaining flexible and cost-effective.

To meet all of the criteria in an ever-accelerating production environment, developers rely on software testing, which is one of the keys to staying ahead of industry progress. In this article, I will discuss why testing is necessary as well as the best testing practices, tools, and frameworks in Java.

Why Is Testing Necessary?

Software testing assists in quickly detecting and resolving all bugs and issues to ensure product quality prior to exposing it to the clients, which is critical for gaining customer satisfaction and trust.

Here are key reasons why testing can help in the development of top-notch software:

1. A test is the simplest way to ensure that your code behaves as expected. By creating various scenarios and asserting expected outcomes, you can ensure that a specific block of code produces the desired results under specific conditions.

This is especially important in the case of an existing system because it shows you whether or not the changes you make will break functionality that is already there.

2. A test serves as a safety net for engineers working in a collaborative setting. In this case, a developer frequently works with code that they did not write in the first place. To ensure that the code's behavior remains unchanged (or changes as planned), the developer can run existing tests to avoid unintended side effects.

This helps in avoiding changes which aren’t desired, as well as in giving the developer more confidence and enabling them to modify software quicker and in a more reliable way.

3. A test, in addition to comments and traditional documentation, provides a useful form of documentation by clearly and instantly demonstrating how a specific function or method should work in various scenarios.

4. A test adds another layer of verification, reducing reliance on Quality Assurance (QA) teams, which frequently play an important role in the software development process. By cleverly implementing testing practices, developers can address a large number of potential issues before the code even reaches QA.

This results in shorter iteration cycles and allows QA to concentrate on higher-level, often more complex, system-wide testing scenarios. And, due to less QA resources required for earlier stages of testing, this helps in saving time and money for the company.

What Are the Best Testing Practices?

Development cycle speed is one of the foundational factors of a project's success in the digital age. This is why testing code as soon as it is written is one of the best practices in software development.

It allows you to catch and address bugs early in the development process, which is much more cost-effective and efficient. If you discover a problem during the initial coding phase, you will most likely only need a few minutes to fix it.

In contrast, fixing a bug that has made its way into production can be a time-consuming process, especially if it involves client-side updates or even OS-level changes. In this case, correcting an error can degrade user experience and potentially harm the company's reputation.

An example of this, taken to the extreme, would be a bug in the software of a rocket that has already launched. Even if we understand there is a bug when the rocket starts moving (the code has made its way to production and is now used), it will probably be impossible to fix and avoid catastrophic consequences.

The Test-Driven Design (TDD) approach takes the concept of rapid testing to its logical conclusion. It requires the creation of tests even before the actual code is written. The typical TDD cycle consists of the following steps:

1. Creating a test for a new functionality. This test will initially fail because the code to fulfill the test's requirements does not yet exist.

2. Writing the bare minimum of code required to pass the test to encourage simple and focused code solutions.

3. Refactoring code to improve its structure while maintaining its functionality.

TDD guarantees that the code is continuously tested against its requirements. Furthermore, because tests are written first, TDD ensures that all code has corresponding test coverage, reducing the possibility of undiscovered bugs slipping through the cracks. All of this results in more robust, reliable software and a more maintainable codebase.

What Java Test Types Are There?

The following tests are commonly used to ensure an efficient and robust software testing process in Java:

Unit Tests

These fundamental tests ensure the functionality and dependability of individual Java application components. During unit testing, dependencies or other layers are typically "mocked" to ensure separate components are isolated so that the focus remains solely on the unit under test.

Unit tests are one of the most common types of tests in an application because they cover the majority of scenarios and edge cases and can be performed quickly and easily.

In Java, a set of tools, each serving a specific purpose, aids in the execution of unit tests. JUnit is Java's primary testing framework, providing annotations and assertions for defining and validating test methods.

Mockito, a mocking framework, is useful when it is necessary to simulate and isolate external dependencies. It works in tandem with JUnit, with specific runners and annotations designed to make mocking in JUnit tests easier.

Hamcrest provides a collection of expressive matchers for more descriptive assertions. When standard mocking proves inadequate, particularly with static methods or final classes, PowerMock provides enhanced capabilities.

However, it is worth noting that if the code requires mocking static methods or final classes, it may be a good idea to refactor it to enhance testability by, for example, introducing dependency injection and mocking instance method calls, rather than relying on static/utility classes and functions.

Integration Tests

After ensuring that separate application components function properly, tests to see how they interact with one another within an integrated system are performed. These tests are more complex than unit tests due to their scope.

They are, however, less common: they may test some specific scenarios and, on occasion, a few edge cases.

Due to the complexity of setting up and running integration tests in Java, specialized tools and frameworks are frequently required. JUnit, which is widely used for unit testing, can serve as a foundation for integration tests due to its adaptable annotations and assertions and can be used in conjunction with Mockito.

Spring Test is essential for Spring-based applications, providing a stable environment for genuine integration testing. For Spring-based applications, the @RunWith(SpringJUnit4ClassRunner.class) annotation can be used to bring up the application context during tests.

End-to-End Tests (E2E)

These tests, also known as acceptance tests, are essential for confirming that the entire application or system functions properly. They provide a comprehensive understanding of how the system works, from user interfaces to complex back-end processes.

Their significance stems from their one-of-a-kind ability to replicate real-life user interactions, validating each step and ensuring the smooth operation of critical business processes. E2E tests, which are more complicated and less common than unit and integration tests, validate main user flows rather than corner cases.

In essence, they test the system as a whole, assuring developers and stakeholders that the code is fully ready for production.

E2E testing in Java requires a production-like environment, complete with specific test data that mimic real-world scenarios. It’s hard to pick one technology to recommend since E2E testing strongly depends on the nature of the service being tested and external resources.

However, libraries like Unirest could be used to facilitate testing REST APIs of the service, and external dependencies, like databases or queues, can be mocked with the help of local Docker images.

UI Tests

This type of testing is required for applications with user interfaces. UI tests, which are typically the most time-consuming to write and run, ensure that the user-facing components of an application behave as intended, providing both functionality and a positive user experience.

The essence of these tests is their ability to validate user interactions, visual elements, and overall flow, ensuring that the software meets its design requirements and is free of bugs.

Selenium is the de facto tool for UI testing in Java. It enables developers to simulate real-world user interactions and validate the UI's behavior by automating browser activities.

While JUnit is primarily used to streamline unit tests, it also provides a familiar setting for structuring UI tests when combined with Selenium.

Testing Pyramid

All of the aforementioned types of testing can be used to create a visual representation of the ideal distribution of test types, known as the Testing Pyramid. Its foundation consists of numerous and fast units. As you progress up the pyramid, you encounter more time-consuming and complex tests, such as integration, end-to-end, and UI tests.

For unit, integration, end-to-end, and UI tests, an ideal distribution might be 60/20/15/5. If there are no UI tests, a 60/30/10 ratio can be used. While broad system behaviors are tested, this pyramid approach ensures that there is also a strong foundation of fast, focused tests to catch issues at the initial stages, promoting efficient and effective testing.

As one of the most popular programming languages, Java has a broad testing ecosystem with tools and frameworks that cater to various testing needs.

Using these tools, as well as the practices described in this article, you can greatly accelerate the development cycle while improving the maintainability and quality of the systems and applications you create. These factors are critical for success in the fast-paced modern digital industry.